1. Field of the Invention
This invention relates generally to the field of prefabricated structural members and, specifically, to structural slabs which are used as surface and bridge deckings that are attachable to, and removable from structural inposts and supports such as steel beams or girders. The methods and articles of this invention include methods for prefabricating slabs, the articles themselves containing novel attachment means, and methods for acquiring a physical coupling of these slabs to supporting beams or girders.
2. Description of the Background and Relevant Art
It has been common in the road and bridge construction industry to build roadway surfaces and bridges by use of (concrete) deck slabs that have been cast in situ and are used to span, and are supported by, other structural steel or concrete supports girders. Improvement to the above method has been had by attaching the slabs in a manner by which they cooperate structurally with the supporting members. This improvement is termed "composite construction" and has proven to increase the efficiency and effectiveness of the supporting members. The cast in situ method of bridge deck construction, with all of its advantages, carries with it some significant disadvantages. One such disadvantage is that the method requires a great deal of time in order to build forms, pour and cure the concrete. Another obvious disadvantage is that field conditions such as inclement weather, make it difficult to achieve a high degree of quality, durability and expediency.
Precast concrete slabs have long been viewed as desirable elements to use in bridge deck construction. Such slabs are generally prefabricated off-site, under factory controlled conditions, and result in the production of high quality concrete decks. Since they may be generally produced well in advance of the use requirement, they may be stock-piled and prepositioned at the site of construction. During actual roadway/bridge construction with the precast concrete slabs, traffic time is interrupted only for a relatively short period while the deck units are placed into position.
Slab interconnection does not prove as great a problem as connection of the slab to the underlying structure. Where the slabs or deck portions (if gratings rather than slabs are used) have had extensions or protrusions from the margins thereof, connection means are not a problem. As early as 1939, U.S. Pat. No. 2,162,742, was issued to H. Nagin for a flooring construction. Nagin taught a metal grid structure which was used as deck surface for a bridge. He showed the use of (elongate) thin metal (strips) plates to construct a form for a grout receiving region atop an underlying girder. Although it did not appear to be Nagin's intent to provide a form for grout which would effect actual connection between the deck sections, his formation of a grout receiving area presaged the modern use of grout to provide support and mechanical coupling between deck slabs or gratings and the supporting structure. Further to Nagin's credit was the use of metal strips, slotted to fit between grid stringers, to form the sides of the grout receiving mold. The strips are held by friction and thus are not rigidly attached (nor attachable), to the grid or deck. Unfortunately, Nagin went no further with the grout form of his disclosure and it would appear to have little application to today's precast concrete or composite slab. Further, the Nagin grouting concept did not entertain use of the grout as a support for the deck system and a means for securing the deck slabs to the underlying support structure. Thus, a cost-effective, structurally sound and versatile method of attaching slabs to supporting members has been a long-sought goal in the construction industry.
Many methods of attachment have been devised for securing bridge deck slabs, in particular, to underlying support structures. These methods range from simply bolting the slabs to the girders to more sophisticated welded type connectors. King, in U.S. Pat. No. 4,977,636 teaches a bridge support system in which a cap member is used in combination with a temporary base support surface to form an enclosed area between a bridge deck and a support column. The enclosed region inwardly receives reinforcing rods and is eventually filled with concrete as it is poured over the deck structure. Thus, the deck structure or slab members are actually an underlayment and would not themselves serve as a traffic-contacting road surface. Yet, the King teaching clearly provides a non-adjustable haunch region that is a corollary of the earlier Nagin art. In this instance, however, the original deck slabs (underlayment) are physically coupled to their supporting structure and each other by a continuous concrete extension of the roadway surface. Significant disadvantages are realized in the King embodiment in that: firstly, a special support surface form must be constructed to receive the concrete; and secondly, some of the support surface must be removed thereafter.
A patent issued to Slaw, Sr., U.S. Pat. No. 4,972,537, disclosed, in late 1990, a composite prefabricated deck panel and a method of construction therefor. Slaw, Sr. discloses the use of metal connecting rods to secure prefabricated deck panels to an underlying support structure. Haunch type enclosed areas are formed between the underside of the panels and the top of each of several girder support members. Located within each enclosed area is a plurality of metal connectors. Once the panels are properly positioned, grout is pumped into the enclosed areas to permanently secure the panels to the support members. According to the Slaw, Sr. teaching, the sides are preformed in the deck sections and rest atop a girder with a flexible seal therebetween. Nonadjustable, preformed concrete shoulders serve as the sides of a haunch mold and depend from the deck panels proper. As in the case of King, Slaw, Sr. does not provide, in the prefabricated panels, a means for acquiring an adjustable haunch mold. Instead, the aforesaid concrete shoulders rest ontop the supporting girder or beam and require a seal therebetween in order to ensure containment of the grout that is to be pumped into the haunch region.
Final to this discussion of relevant art is the patent issued to Eskew et al. in mid 1991, U.S. Pat. No. 5,025,522. Essentially, these patentees teach a bridge deck panel support system and method for supporting precast bridge deck panels on a bridge girder. The deck panels are initially supported through a grout layer that is located between the bottom of the panel and the top of the structural support member. An elongate anchor plate atop, and partially girdling, the beam top surface bears an ascending flange, termed "a plate", by Eskew et al., and which, on each side thereof, anchors a grade bar. A continuous seal between the grade bar completes, with a grout filler (placed between the bar and beam), an enclosure or haunch region that is to be filled with concrete. An alternate embodiment eliminates the grade bar and uses the ascending plate or flange member only. Once the panel members have been properly positioned, they rest on a seal means placed between (preferably) the grade bar and the undersurface of the panels. Concrete from an overlay then fills the enclosed (haunch) area between the adjacent plate members and their support. As with the preceding art, a most notable disadvantage of the Eskew et al. teaching is the lack of an easily made mold or form that may be used to create a haunch region that is defined by the top surface of the support member (girder), adjustable form sides and the overlaying and haunch filling with concrete.
Some of the aforesaid attachment methods have been successful from an attachment standpoint, but most, if not all, methods have failed to provide a method of attachment which allows the top or the bottom of the panel to be attached to match a predetermined grade or elevation. To compensate for this deficiency, a concrete topping is generally poured over the slab to provide a uniform surface which meets predetermined grade and elevation requirements. This cast in situ topping requires a significant amount of cure time before the structure may be used.
Additional to the aforementioned grading problem, most of the previous attachment methods have also failed to allow the slab and structural support member to act cooperatively as a composite structure. Some methods do achieve partial composite action, as may be seen in the discussion of relevant art; but, they fail to adequately convince bridge construction engineers that full composite action is developed. In compensation for this deficiency, larger structural support members are currently being used. Still, a further disadvantage of presently used support systems is recognized in relation to the structural supporting members themselves. These members deflect significantly when loads are placed upon them and their final geometry is not realized until all of the precast slabs are situated in final position. Thus, the top surface of the structural supporting members, and therefore the surface of the tops of all of the slabs, is not defined until all of the slabs have been placed on the structural members. I am unaware of any modern and reliable system that offers postplacement adjustment of the tops of the slabs (roadway surface) to the proper elevation.